ProMaster Van Plumbing: Water Systems, Tanks & Setup

Why Is the ProMaster One of the Best Vans for Plumbing?

Two things set the RAM ProMaster apart when it comes to plumbing: a completely flat floor and front-wheel drive. Most cargo vans have a raised hump or driveshaft running underneath, which limits where you can mount tanks and route plumbing lines.

The ProMaster doesn't have that problem. The flat underbody gives you a clean path to mount freshwater and greywater tanks underneath the van — keeping them out of your living space entirely. Front-wheel drive also means no driveshaft tunnel eating into your floor, so water lines can run where they need to without awkward workarounds.

We build ProMaster conversions at our San Diego, CA shop and see these advantages play out on every plumbing install. For a broader look at van plumbing across all platforms, check out our plumbing systems overview.

How Does the Freshwater System Work in a ProMaster Van?

Your freshwater system is the starting point for the entire plumbing layout. It includes the tank, a 12V water pump, filtration, and all the supply lines running to your sink, shower, and any other fixtures.

• • Tank sizing: Most ProMaster builds carry 20 to 40 gallons of fresh water. A solo traveler can stretch 20 gallons for a week with careful use. Couples or full-timers usually want 30 to 40 gallons.
• • Tank placement: The flat underbody is ideal for mounting a tank between the frame rails. This keeps weight low and centered, and frees up interior space. We secure tanks with custom brackets and protect fill/drain ports from road debris.
• • Water pump: A 12V demand pump (like the Shurflo 4008 or Remco) pressurizes the system and kicks on automatically when you open a faucet. We install an accumulator tank to reduce pump cycling and smooth out the water flow.
• • Filtration: A basic sediment filter is standard. For drinking water, we can add a carbon block or multi-stage filter to improve taste and remove contaminants.

How Do You Handle Greywater in a ProMaster Conversion?

Greywater is the used water from your sink and shower. It needs to go somewhere, and a well-designed greywater system keeps things clean and odor-free.

• • Greywater tank: Typically sized to match or slightly exceed your freshwater tank. If you carry 30 gallons of fresh water, a 30- to 35-gallon grey tank gives you a buffer. Mounted underneath the van, same as the fresh tank.
• • Drain routing: All drains run to a common low point using gravity. The ProMaster's flat floor makes routing drain lines straightforward — no fighting with driveshaft humps or frame obstructions.
• • Dump valve: A gate valve underneath lets you empty the grey tank at any dump station. We position it for easy access so you're not crawling under the van.

Why Is PEX the Best Plumbing Material for Van Conversions?

All of our van plumbing uses PEX (cross-linked polyethylene) tubing. It's the standard for van conversions and for good reason:

• • Vibration-resistant: PEX flexes with the movement of the van. Rigid copper or CPVC would crack at the joints over time from road vibration.
• • Freeze-tolerant: PEX can expand slightly if water inside freezes, which reduces the chance of burst pipes compared to rigid materials. It's not freeze-proof, but it gives you more margin.
• • Easy to route: PEX bends around corners without fittings, which means fewer potential leak points. In a van where space is tight and everything vibrates, fewer connections = fewer problems.
• • Lightweight: Every pound matters in a van. PEX weighs a fraction of what copper does.

We typically use 1/2" PEX for main supply lines and 3/8" for fixture connections, with crimp or SharkBite fittings depending on the run. If you want to learn the full process, our van plumbing guide walks through it step by step.

How Do You Winterize Plumbing in a ProMaster Van?

If you plan to travel in freezing temperatures, your plumbing system needs to handle it. We design with winterization in mind from the start — not as an afterthought.

• • Low-point drains: Every plumbing line has a drain at its lowest point so you can fully empty the system when needed.
• • Bypass valves: The water heater gets a bypass so you can winterize the supply lines without running antifreeze through the heater.
• • Compressed air blowout: We plumb the system so you can attach a compressor and blow all the water out of the lines in a few minutes.
• • Insulated tank enclosures: For four-season builds, we insulate the underbody tanks and can add heat tracing (electric heating cable) to keep lines from freezing when the van is parked in cold weather.

How Much Does ProMaster Van Plumbing Cost by Build Tier?

Plumbing costs vary based on the scope of the system. Here's a rough idea of what to expect at each tier:

These are approximate ranges — every build is custom, and your actual cost depends on the specific components and layout. For the full cost picture, see our ProMaster conversion cost breakdown.